package org.example.java.nio;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

public class CopyFile {
  public static void main(String[] args) throws Exception {
//    String infile = "data\\ml-1m\\ml-1m\\ratings.dat";
    String infile = "data\\ml-10m\\ml-10M100K\\ratings.dat";
    String outfile = "data\\copy.txt";
    File file = new File(outfile);
    if (file.exists() && file.delete()) {
      System.out.println("copy file delete success.");
    }
    long start = System.currentTimeMillis();
    // 获取源文件和目标文件的输入输出流
    FileInputStream fin = new FileInputStream(infile);
    FileOutputStream fout = new FileOutputStream(outfile);
    // 获取输入输出通道
    FileChannel fcin = fin.getChannel();
    FileChannel fcout = fout.getChannel();
    // 创建缓冲区
    ByteBuffer buffer = ByteBuffer.allocate(1024);
    while (true) {
      // clear方法重设缓冲区，使它可以接受读入的数据
      buffer.clear();
      // 从输入通道中将数据读到缓冲区
      int r = fcin.read(buffer);
      // read方法返回读取的字节数，可能为零，如果该通道已到达流的末尾，则返回-1
      if (r == -1) {
        break;
      }
      // flip方法让缓冲区可以将新读入的数据写入另一个通道
      buffer.flip();
      // 从输出通道中将数据写入缓冲区
      fcout.write(buffer);
    }
    System.out.println("Spend: " + (System.currentTimeMillis() - start) + "ms");
  }
}